In recent years, in aerospace fields and environmental and energy fields, highly reliable materials have been desired which are excellent in heat resistance and high in both heat insulation property and mechanical properties, in order to achieve higher efficiency and higher energy. Candidate materials therefor include inorganic fiber-bonded ceramic materials as an example. The inorganic fiber-bonded ceramic materials are insensitive to defects and high in fracture resistance, as compared with simple ceramics. In addition, the inorganic fiber-bonded ceramic materials are highly dense as compared with ceramic fiber-reinforced ceramic-matrix composites (CMC) produced by chemical vapor infiltration methods (CVI methods) or polymer infiltration and pyrolysis methods (PIP methods), and subjected to machining to provide high surface smoothness.
Such an inorganic fiber-bonded ceramic material is disclosed in, for example, Patent Literature 1. Briefly, the inorganic fiber-bonded ceramic material described in Patent Literature 1 is obtained by applying hot pressing under high temperature and pressure to a laminate of ceramic fibers containing, as their main constituent, Si-M-C—O (M represents Ti or Zr) covered with a surface layer containing SiO2 as its main constituent, and in the hot press process, some C in the Si-M-C—O fiber is produced on the fiber surface, and further, M in the Si-M-C—O fiber reacts with C to provide a structure including fine particles of MC dispersed in the inorganic substance. Accordingly, the structure of the inorganic fiber-bonded ceramic material is created in the hot press process under high temperature and pressure with the use of a pyrolysis reaction of the raw fiber. In other words, in order to obtain a favorable inorganic fiber-bonded ceramic structure, it is necessary to rigorously control the pyrolysis reaction in the hot pressing process.